1. Field of the Invention
The present invention relates to a plasma display panel, and more particularly, to a method of driving a plasma display panel and an apparatus thereof enabling to minimize power consumption for driving the plasma display panel.
2. Discussion of the Related Art
Generally, a plasma display panel (hereinafter abbreviated PDP) is more advantageous for enlarging its screen size than any other flat board type display devices.
Therefore, PDP gets lots of attention as a large-sized display panel.
PDP, as shown in FIG. 1, is mainly driven by an AC voltage with three electrodes, which is called an AC surface discharge type PDP.
FIG. 1 illustrates a bird's-eye view of a discharge cell in a 3-electrodes AC surface discharge type PDP (AC PDP of surface discharge type having 3-electrodes) according to a related art.
Referring to FIG. 1, a discharge cell in a 3-electrodes AC surface discharge type PDP includes scan and sustain electrodes 12Y and 12Z formed on a front substrate 10 respectively and an address electrode 20X formed on a back substrate 18.
A front dielectric layer 14 and a protective layer 16 are stacked on the front substrate 10 on which the scan and sustain electrodes 12Y and 12Z are formed in parallel with each other. And, wall charges are accumulated on the front dielectric layer 14.
The protective layer 16 prevents the front dielectric layer 14 from being damaged by sputtering generated from plasma discharge as well as increases a discharge efficiency of secondary electrons. And, the protective layer 16 is generally formed of MgO.
On the back substrate 18 having the address electrode 20X, formed are a back dielectric layer 22 and barrier ribs 24. And, phosphors 26 are coated on surfaces of the back dielectric layer 22 and barrier ribs 24.
The address electrode 24 is formed to cross with the scan and sustain electrodes 12Y and 12Z.
The barrier ribs 24 are formed to be in parallel with the address electrode 20X so as to prevent UV and visible rays from leaking in an adjacent discharge cell.
The phosphors 26 become excited by the UV-rays generated from plasma discharge so as to irradiate one of red, green, and blue visible rays. An inert gas for gas discharge is injected in a discharge space provided between the barrier ribs 24 and two substrates 10 and 18.
The above-explained discharge cell is selected by a confronting discharge between the address and scan electrodes 20× and 12Y, and then maintains the discharge state by a surface discharge between the scan and sustain electrodes 12Y and 12Z so as to be at a sustain discharge state.
In PDP, the phosphors 26 emit light so as to discharge visible rays outside the cell. In this case, PDP adjusts a discharge maintaining time, i.e. discharge maintaining time, of the cell in accordance with video data so as to realize a gray scale required for displaying a video.
In such a 3-electrodes AC surface discharge type PDP, a driving time for displaying a specific gray scale of a single frame is divided into a plurality of sub-fields. For each sub-field duration, luminescence is generated in proportion to a count of a weight of the video data so as to carry out a gray scale display.
In order to display such a gray level of a video, a general PDP is driven by an ADS (address and display period separated) system of dividing a single frame into sub-fields having different discharge counts.
For instance, in case that a video is displayed with 256 gray scales using video data of 8 bits, a 1-frame display duration (ex. 1/60 second=about 16.7 msec.) in each discharge cell is separated into eight sub-fields.
And, each of the eight sub-fields is separated into a reset period, an address period, and a sustain period. A time weight is differently given to the sustain period of each of the eight sub-fields in proportion to 2N, where N=0, 1, 2, 3, . . . , 7. Namely, each of the time weights of the first to eighth sub-fields increases like a ratio of 1:2:4:8:16:64:128.
Since the sustain periods of the sub-fields become different from each other, the gray scale of the video can be expressed.
FIG. 2 illustrates a graph of driving waveforms applied to electrodes respectively for driving PDP according to a related art.
Referring to FIG. 2, a PDP driving is divided into a rest period initializing discharge cells, an address period generating a selective address discharge in accordance with a logic value of video data, a sustain period maintaining the discharge in the discharge cell from which the address discharge is generated, and an erase period erasing all the discharges maintained in the entire discharge cells. More specifically, the reset period equalizes the states of the entire discharge cells by initializing the discharge cells, the address period selects specific ones of the discharge cells, and the sustain period expresses the gray scale in accordance with the maintaining discharge count.
The reset period is divided into a set-up period and a set-down period. In the set-up period, an ascending ramp wave ramp1 is supplied to the scan electrode 12Y, while a descending ramp wave ramp2 is supplied to the scan electrode 12Y.
During the set-up period, a weak reset discharge is generated by the ascending ramp wave ramp1 so that wall charges are accumulated in the cell.
During the set-down period, the wall charges in the cell are properly erased in part by the descending ramp wave ramp2 so as to be reduced as helping a following address discharge as well as prevent a wrong discharge. Besides, in order to reduce the wall charges, a pulse having a positive (+) DC voltage Va is applied to the sustain electrode 12Z during the set-down period.
Against the sustain electrode 1X supplied with the pulse of the positive DC voltage Va, the scan electrode 12Y supplied with the descending ramp wave ramp2 becomes negative (−). Thus, inversion of the polarities makes the wall charges, which were generated from the set-up period, are reduced.
During the address period, an address discharge is generated by a pulse of a scan voltage V_scan applied to the scan electrode 12Y and a data pulse applied to the address electrode 20X. The address discharge enables to maintain the previously generated wall charges for a period of other discharge cells to be addressed. In this case, a voltage level of the pulse of the scan voltage V_scan is greater than or equal to a ground potential.
During the sustain period, a trigger pulse TP is initially applied to the scan electrode 12Y. A sustain discharge of the discharge cells having the wall charges sufficiently for the address period is initiated by the trigger pulse TP. Subsequently, sustain pulses SUSP are applied to the scan and sustain electrodes 12Y and 12Z alternately so as to sustain the sustain discharge. Thus, the sustain discharge is maintained so as to display a demanded gray scale.
And, during the erase period, an erase pulse EP is applied to the sustain electrode 12X so as to stop the sustained discharge. The erase pulse EP has a ramp wave so as to have a small luminescent size as well as has a short pulse width so as to erase the discharge. Since the short erase discharge is generated by the erase pulse EP having such a short pulse width, the charged particles are erased so as to stop the discharge.
In the above-explained driving periods, a sufficiently large quantity of wall charges is formed with the weak discharge using the ramp waves ram1 and ram2 during the reset period, and the a proper quantity of the wall charges is erased. The erased wall charges are used for the following address discharge.
In other words, the wall charges are formed uniformly on the entire screen for the reset period, thereby enabling to lower the driving voltage required for the address period.
Unfortunately, in the PDP driving has difficulty in reducing the voltage applied to the address electrode 20X for the address discharge.
Specifically, the address voltage required for the address discharge is expressed by the following Formula 1.
[Formula 1]
Vaddress>Vf,y-a−(Vw,d+Vw,y, where Vaddress, Vw,d, Vf,y-a, and Vw,y are a address voltage, a wall voltage accumulated on the address electrode 20X, a discharge initiating voltage between the address and scan electrodes 20X and 12Y, and a wall voltage accumulated on the scan electrode 12Y, respectively.
In Formula 1, providing that a minimum point of the scan voltage V_scan, as shown in FIG. 2, is tied to the ground voltage level, the discharge initiating voltage Vf,y-a is expressed by the data voltage applied to the address electrode 20X only.
In this case, the discharge initiating voltage Vf,y.a as the data voltage is reduced so as to bringing about the problems such as the wrong discharge and the like.
Since the minimum point of the scan voltage V_scan is limited to the ground voltage level, it is difficult to reduce the data voltage as the discharge initiating voltage of the address discharge.